This invention generally relates to macromineral dietary factors with respect to ruminant nutrition. More specifically this invention relates to the effect of dietary cation-anion difference (DCAD) on the health and lactational performance of dairy cows.
Dietary macromineral elements are necessary for proper health and productive performance of lactating dairy cows. As a class of nutrients, these elements have been the subject of extensive research, and considerable information exists about individual effects of each micromineral element. Information on interrelationships of macromineral elements in diets for lactating dairy cows is relatively limited.
An early publication was the first to propose that mineral interrelations were related to acid-base status [J. Biol. Chem., 58, 235 (1922)]. It was proposed further that maintenance of normal acid-base equilibrium required excretion of excess dietary cations and anions. It was hypothesized that consumption of either excess mineral cations relative to anions or excess anions relative to cations resulted in acid-base disturbances in animals (A. T. Shohl. Mineral Metabolism. Reinhold Publishing Corp., New York. 1939).
Once animal nutritionists began to test this hypothesis, mineral interrelationships were found to affect numerous metabolic processes, and there was evidence that mineral interrelationships had profound influences. It was theorized that for an animal to maintain its acid-base homeostasis, input and output of acidity had to be maintained. It was shown that net acid intake was related to the difference between dietary cations and anions. The monovalent macromineral ions Na, K and Cl were found to be the most influential elements in the interrelationship (P. Mongin. Page 1, Third Ann. Int. Mineral Conf. Orlando, Fla. 1980).
Nutrient metabolism in animals results in the degradation of nutrient precursors into strong acids and bases. In typical rations fed to dairy cattle, inorganic cations exceed dietary inorganic anions by several milliequivalents (meq) per day. Carried with excess dietary inorganic cations are organic anions which can be combusted to HCO.sub.3.sup.-. Consequently, a diet with excess inorganic cations relative to inorganic anions is alkalogenic, and a diet with excess inorganic anions relative to cations is acidogenic.
Chloride is the most acidogenic element to be considered. An excess of dietary chloride can lead to a respiratory and/or metabolic acidosis. The acidogenic influence of chloride can be negated by sodium and potassium which are alkalogenic elements. Conversely, excess intake of sodium or potassium can induce metabolic alkalosis.
Blood pH ultimately is determined by the number of cation and anion charges absorbed in the blood. If more anions than cations enter the blood from the digestive tract, blood pH will decrease. It was proposed that a three-way interrelationship among dietary Na, K and Cl, i.e., the sum of Na plus K minus Cl [in meq per 100 g diet of dry matter (DM)], could be used to predict net acid intake. The term "dietary cation-anion difference (DCAD)" was coined to represent the mathematical calculation (W. K. Sanchez and D. K. Beede. Page 31, Proc. Florida Rum. Nutr. Conf. Univ. of Florida. 1991). Expressed in its fullest form, DCAD is written as follows: EQU meq [(Na.sup.+ +K.sup.+ +Ca.sup.+2 +Mg.sup.+2)-(Cl.sup.- +SO.sub.4.sup.-2 +PO.sub.4.sup.-3)]/100 g of dietary dry matter (DM).
A problem with including the multivalent macrominerals (Ca, Mg, P and S) in the DOAD expression for ruminants relates to the variable and incomplete bioavailability of these ions compared to Na, K and Cl. The expression employed most often in non-ruminant nutrition is the monovalent cation-anion difference: EQU meq (Na.sup.+ +K.sup.+ -Cl.sup.-)/100 g dietary DM
Because of the additional use of sulfate salts in prepartum rations, the expression that has gained most acceptance in ruminant nutrition is as follows: EQU meq (Na.sup.+ +K.sup.+)-(Cl.sup.- +SO.sub.4.sup.-2)/100 g dietary DM
For a calculation, mineral concentration are first converted to milliequivalents: ##EQU1##
The following illustrates a calculation of the meq Na+K-Cl-S value of a diet with 0.18% Na, 1.0% K, 0.25% Cl and 0.2% S. There are 180 mg Na (0.18%=0.18 g/100 g or 180 mg/100 g), 1000 mg K (1.0% K), 250 mg Cl (0.25% Cl) and 200 mg S (0.2% S) per 100 g dietary DM. The SO.sub.4.sup.- entity is calculated as atomic sulfur. ##EQU2##
The calculated DCAD value is as follows: EQU meq (Na+K-Cl-S)=7.8+25.6-7.0-12.5=13.9 meq/100 g dietary DM
A simpler expression is as follows: ##EQU3##
A study was conducted which was designed specifically to evaluate the effect of DCAD on acid-base status and lactational performance of dairy cattle. Diets formulated with -10, 0,+10 or +20 DCAD were compared. A diet with +20 improved dry matter intake (DMI) 11% and milk yield (MY) 9% compared with a -10 DCAD diet. Blood bicarbonate (HCO.sub.3.sup.-) increased linearly with increasing DCAD, which indicated an improvement in acid-base status with high DCAD compared with low DCAD. It was concluded that responses to increasing DCAD were independent of specific Na, K and Cl effects [J. Dairy Sci., 71, 346 (1988)].
Another study evaluated the influence of Na, K and Cl at constant DCAD. Diets were formulated to provide +32 DCAD in (1) a basal diet adequate in dietary Na, K and Cl; (2) a basal diet containing an additional 1.17% NaCI; and (3) a basal diet containing an additional 1.56% KCI. Fifteen midlactation cows were assigned to replicated 3.times.3 Latin squares. The KCI-fed cows consumed more DM and had a lower milk fat percentage than NaCI-fed cows, but there were no differences in milk yield. It was concluded that dietary DCAD was a more important determinant of dietary impact on systemic acid-base status than actual dietary concentrations of Na, K and Cl [(J. Dairy Sci., 73, 3485 (1990)].
An extensive study was conducted with 48 cows and 15 dietary treatments to investigate lactational and acid-base responses to DCAD as [(Na+K)-(Cl+S)]. DCAD ranged from 0 to +50 [(Na+K)-(Cl+S)]/100 g dietary DM. The basal diet was 54.5% concentrate, 5.5% cottonseed hulls, and 40% corn silage (DM basis). Dry matter intake (DMI) and milk yield (MY) was highest when DCAD was between +17 to +38, and +25 to +40, respectively [J. Dairy Sci., 77, 1661 (1994)].
In another study three switchback experiments were conducted with 12 cows each in early, mid or late lactation. Increasing DCAD from +5.5 to +25.8 in early lactation, and from +14 to +37.3 in midlactation, increased DMI and milk production. These effects were not observed in late lactation when +20 was compared to +37.5 DCAD. The study results supported the concept that response to DCAD is affected by stages of lactation [J. Dairy Sci., 78, 2259 (1995)].
The cumulative DCAD studies indicate that dietary K has a unique role, particularly during heat stress in dairy cows. When potassium carbonate was the source of dietary K, a linear response to dietary K in heat stressed dairy cows was observed. Every 1% increase in K raised fat-corrected milk by 8.9 lbs/day [J. Dairy Sci., 69, 124 (1986); 70, 81 (1987); and 70, 309 (1987)].
The reported studies have established the DCAD concept as an important factor in diet regimen for dairy cows. There are contradictions in the overall DCAD data reported in the literature, so that salient DCAD considerations are incentive for continued investigation.
Accordingly, it is an object of this invention to provide a method for improving the lactational performance of dairy cows.
It is another object of this invention to provide a method for DCAD control to increase the dry matter intake (DMI) of lactating dairy cows.
It is another object of this invention to provide a method for DCAD control to increase the milk yield (MY) of lactating dairy cows.
It is another object of this invention to provide a method for DCAD control to increase the blood bicarbonate (HCO.sub.3.sup.-) of lactating dairy cows.
It is a further object of this invention to provide a feedstock for improving the lactational performance of dairy cows, which comprises a supplemented basal ration having a prescribed content of micromineral nutrients, and which is formulated without an incipient chemical heat generation in the basal ration matrix.
Other objects and advantages of the present invention shall become apparent from the accompanying description and example.